Thursday, December 31, 2009

The broad mainstream tradition of space SF tradition is to treat planets as analogous to island countries, with their surrounding orbital space as 'offshore waters.' In the more picaresque settings an occasional orbital station around some backward colony planet might become a Free Haven, welcoming all comers with no questions asked and fewer answered. But as a rule, any planet that wants to count for anything controls its own orbital space. Or at least someone does, such as a trade federation.

In this type of setting, where entire regions of local space are normally under a single authority, any enemy must come from some other local region, arriving from deep space. The attackers might come from Mars, or Callisto, or Sigma Draconis IV, without really changing the story line.

And much of what I have said here follows from that assumption. An approaching deep space force can be detected at Stupendous Range, its orbit telegraphing its region of origin and therefore probably its intent. It can then be engaged at merely Enormous Range, at the translunar fringe of orbital space or even beyond.

But what if both the attacker and defender are in Earth orbital space to begin with?

In Cold War days there was a whole subgenre that dealt with orbital warfare, in a near future setting - back when that meant circa 1965 - and a Cold War context. Much more recently a micro-genre of alternate history rocketpunk has appeared, centering on World War II. The most notable example is Ministry of Space, but I believe there are others.

In fact an all out war between Earth powers would reduce Earth's inner orbital space to a no man's land. Low orbit is too vulnerable to surface-launched kinetics, and shuttle types are especially vulnerable during ascent and return. Forces in high orbit or deep space would be cut off from their home bases for the duration, on both sides. In an early-space setting they'd have plenty on their hands to survive, let alone conduct operations against each other.

But suppose that, in a century or two, Earth orbital space is home to a welter of stations, habs, ships, and other platforms. Some belong to national governments, some are jointly operated (like the ISS today), or belong in various ways to a host of entities such as NGOs and private firms. Over time, how these spacecraft are 'flagged' may have as little to do with actual ownership as it does at sea today.

Ships at sea have to put into port sooner or later, entering someone's territorial waters. Spacecraft, other than shuttle types, remain in space, merely docking with other spacecraft from time to time. In these circumstances, so long as someone can pay the bills a flag of convenience is barely short of outright autonomy.

Independent or quasi-independent space habs are as plausible in Earth orbital space (or Mars, etc.) as they are in the asteroid belt, and perhaps more so. The asteroids have raw material, but Earth and its orbital space have the markets (and source of immigrants). If cycler ships are used, Earth orbital space is probably the one destination they all call at each time around.

Most likely an ambiguous welter of authority in space will merely provide billable hours for lawyers. But if Earth orbital space is home to increasingly autonomous powers, they can have rivalries, crises, and potentially warfare. What would a war between rival stations or habs in Earth orbital space be like?

It would have to be 'limited,' because of the great vulnerability of spacehabs to attack. But this is true of civil space infrastructure wherever it is located, so it does not distinguish orbital warfare from any other kind of space warfare. Or, in the postnuclear age, from any kind of warfare that any player can hope to survive.

The most obvious difference from the familiar vision of interplanetary (or interstellar) warfare is that travel times are suddenly much shorter. As was noted in the comment thread on orbital combat, mission durations in orbital space look more 'air force' than 'navy.'

The space you are fighting in is also a lot more cluttered, including with neutrals. Of course, 'cluttered' is a relative term. Earth orbital space is vast, taking hours or days to cross at even at orbital speeds. But compared to the months of interplanetary travel it is cheek by jowl. And the clutter may include neutrals whom you do not wish to draw into the war.

Which changes a lot of familiar assumptions. Everyone sees everything? Not behind that big round planet they don't, unless they have an eye on the other side. But even more to the point, we can't see through ships' hulls, let alone human minds, and the change of time scale changes the sort of missions we may undertake.

Imagine a suspicious ship departing a neutral space station.

In a traditional setting, absent magical drives we couldn't do much more than log its orbit. Intercepting and inspecting it would take months. If human inspection is called for you'd need a fairly large ship for long term habitability, and you are committing ship and crew to that one mission for perhaps a year or so. Which means that such missions will be costly, and rare.

Now shift the story into Earth orbital space. Intercept and inspection mission can now be performed in hours to a few days, by a much smaller craft with only short term habitability - which makes such missions far more practical.

For the same reason the 'suspicious spacecraft' itself becomes more plausible. Slipping a covert military craft into the civil traffic flow is cumbersome when civil traffic is months en route. It works a lot better on a time scale of hours to a few days.

Even the manned space fighter starts to be plausible in this environment. Its role is not precisely analogous to an atmosphere fighter, more nearly to a helicopter gunship, for example escorting the craft that carry boarding and inspection teams.

Fighting could and probably will erupt not in the middle of nowhere, but in genuinely crowded space - even amid the constellation of spacecraft that surrounds any large commercial station. A demand is refused, negotiations go pear shaped, and suddenly shooting erupts.

Here we are fighting at Hollywood range, and with civil and neutral craft nearby, posing rules of engagement decisions not to be entrusted to garden variety robotics. Teleoperation is an uncertain option. Jamming can't be ruled out in these close situations - and when split second decisions matter, a little light lag goes a long ways.

This sort of space environment is not confined to Earth orbital space. It can appear wherever you have extensive traffic in a small region of space, with no one local power in a position to regulate it all.

No technological assumptions need to be changed to bring about this state of affairs, only political and social assumptions about who can travel where in space, and whether high traffic local regions of space are typically under a single local authority that can defend them (or attack other local regions) as a unity.

The meta point is that a lot of what I have said here about Realistic [TM] space warfare is driven not just by technology but by (hidden) assumptions about who is fighting and what they are fighting over. Change those assumptions and you may get surprising results.

Wednesday, December 16, 2009

You cannot land on a planet or moon, or leave it - including, notably, Earth - without passing through its surrounding orbital space. This gives orbital space great strategic importance.

I have used 'orbital space' a good deal on this blog without ever defining what it means. Any formal definition would be somewhat arbitrary (like 'the threshold of space') but generally a planet's orbital space is the region dominated by its gravity. Think of it as close enough that you orbit the planet rather than just taking up a nearby solar orbit. (Or orbit a moon instead of its parent planet.)

For orbital space to have distinctive characteristics, major orbit change maneuvers must also require a substantial effort, a delta v of at least a few hundred meters per second - enough that chemfuel burns are costly in propellant consumption, while high specific impulse burns are time consuming.

Ceres, with an escape velocity of 0.51 km/s and low orbit velocity around 0.35 km/s, is about the minimum size for strategically significant orbital space. Neatly, and not entirely by coincidence, this corresponds to the minimum size for a 'dwarf planet,' shaped (literally!) by geological forces.

Significant zones of orbital space thus surrounds the eight major planets, the Moon, Ceres itself, the four big moons of Jupiter, Titan and six other moons of Saturn, four moons of Uranus, and Triton, along with Pluto and a growing list of outer system objects. We are interested in visiting most of them, and might one day be interested in fighting over them. (This last may not really be very likely, but it is possible, and makes for good thud and blunder space stories.)

Earth and Mars have escape velocities of several km/s, on the same order as interplanetary transfer speeds. (Escape speeds from the giant planets are higher still, but in strategic terms their moon systems are like miniatures of the Solar System, and a somewhat different strategic beast.)

This means that typical encounter speeds in Earth and Marsr orbital space are fairly high, even after making the burn from interplanetary transfer orbit. In low Earth orbit, encounter speeds can range from 4 km/s for circular orbits with a 30 degree difference in inclination, up to 22 km/s for a retrograde encounter just below escape velocity. Even at lunar distance a head-on encounter at escape velocity means a relative speed of 2 km/s.

Which makes orbital space a kinetic shooting gallery. A defender can pre-position kinetic target seekers as 'mines' on retrograde orbits, while an attacker coming from deep space needs hardly more than a tap to send kinetics onto a retrograde approach. Moreover, so long as they are below escape velocity, kinetic target seekers will not hurtle off into the void, but keep coming around.

What applies to kinetics also applies to ships. Ships in orbital space do not encounter each other as ships on crossing orbits in deep space do, one flash-past and off they go into the void on their separate paths, needing dozens of km/s of delta v to reverse track and re-engage. Ships orbiting a planet, so long as they are below escape velocity, will swing back around for repeated passes.

And it gets better. Orbital space (specifically, low orbit) is the domain of the Oberth effect. Imagine a target seeker in an elongated elliptical Earth orbit, so that it whips around perigee at 11 km/s, a shade under escape velocity. Let it have a small chemfuel booster good for 3 km/s of delta v. (The booster will have about twice the mass of the target seeker itself.)

Fire the booster at perigee and the target seeker is booted to 14 km/s, well above escape velocity. And its departure speed 'at infinity' will be 8.7 km/s (14 squared - 11 squared). Any target coming from deep space will have its own approach velocity, making for encounter speeds upwards of 12 km/s. A similar boot from low Mars orbit gives a departure speed of 6.2 km/s, and encounter speeds upwards of 10 km/s.

Finally, orbital space has the planet itself at the center of the maelstrom, giving spaceships a rare opportunity to crash, and providing a big exception to the rule that 'everyone sees everything.' You don't see anything through a solid planet or moon, and remote sensor probes can be burned out.

All of this ought to make orbital space militarily ... intriguing. Maneuvering there is more complex than in 'flat' space. Kinetics can be deployed cheaply and effectively as a sort of mine warfare.

And it matters, because a large proportion of strategic objectives will surely be in some planet's or moon's orbital space - or on the planet, subject to attack or blockade by whoever controls its orbital space. In any setting where planets are important, a good case can be made that most combat will take place in their orbital space.

Serious space warfare games, like Attack Vector, respond to all of this potential by avoiding orbital combat like the plague. This is for good reason. No one has yet figured out to sim convincing orbits in a board game, and not for lack of trying. This is no bar to fiction writers, who only have the problem of getting things right, or at any rate convincing.

But there is one other important consideration for orbital combat in a setting. Most of the interesting complications belong only to the near or midfuture, and become progressively less significant at higher techlevels. The planet or moon remains a physical obstacle, but its surrounding winds and currents matter less to steamships, so to speak, than to sailing ships. The shooting gallery effect matters only if kinetics approaching at 3-15 km/s are effective weapons, while orbital maneuvers are trivial for ships with torch drives.

So if you measure speeds as a fraction of c, don't have the captain fretting over approach orbits and defensive orbital mines.

The image is from commenter Luke, via Atomic Rockets. (It actually shows a laser zap, not a kinetic strike, but still portrays realistic orbital combat.)

Related posts: See the June, July, August, and September archives for previous posts in this series, plus the battles of the spherical war cows. And a much earlier post on space fighters.

Sunday, December 13, 2009

It was not mainly about gold, it was about pepper. Europeans used a lot of it, and went to enormous efforts to get their hands on it. Shake or grind it with due respect: If the asteroid belt were known to have anything we want as badly as some of our ancestors wanted pepper, we might already be there.

Gold did figure in at the start, no surprise, and so did Prester John. Persisting rumor or legend placed a Christian kingdom somewhere in India, then a thoroughly vague term meaning 'way off east somewhere.' A Portuguese royal younger son became interested in Prester John, in the rather grubbier African gold trade, and - alas, but you knew it was coming - in the grubbiest African trade of them all.

The age of exploration was on, and one of the first things discovered was original sin.

Henry the Navigator's establishment at Sagres was not a 15th century NASA, and the Portuguese caravel was not a nautical revolution (though it was developed amid an ongoing revolution in nautical technology). In fact the lateen-rigged caravel turned out to be a bit of a technological dead end that faded away in the 16th century.

But what Henry and his shipwrights did was still remarkable; they took a handy, seaworthy type used mainly for deep sea fishing and modified it specifically for exploration. And Henry's captains pushed systematically along the coast of Africa, into waters then unknown to Europeans. They (re-) discovered Madiera in 1420, and the Azores in 1427.

They kept going after Prince Henry died. At last in 1488 Bartolomeu Dias rounded Cape Horn, and the way to the East was open. Ten years later da Gama reached India. The fabled wealth of the East, and especially pepper, was at last in direct reach.

And the world was changed. No need to beat the point to death, but good old Christopher Columbus was just trying to go one better on the Portuguese, armed with a gross underestimate for the size of the Earth and sublime ignorance that there was a continent in the way. Lucky for him there was. But it was the Portuguese who got the ball rolling.

No one, so far as I know, had ever explored before in the systematic way they did. There had been explorers: Pytheas, Hanno the Navigator, and the unnamed, semilegendary Phoenician whose circumnavigation of Africa was reported by Herodotus even though he did not believe it. But those were all one-offs.

The Chinese were doing it just as systematically, and at the same time. Zheng He's last expedition ended in 1433; the Portuguese had already reached the Azores and in 1434 they rounded Cape Bojador, pushing into waters unknown to Europeans since Hanno. It was a remarkable historical coincidence.

Unlike the great treasure junks the caravels were small, perhaps 20 meters long and 50 tons capacity - about a third the length and a thirtieth the displacement of their Chinese contemporaries. Handy and well suited to inshore work, to our eye they seem far better suited to exploration. Columbus thought the Santa Maria was too big and clumsy.

But the comparison is misleading. The Chinese treasure fleets had small handy ships, and more to the point the Chinese fleets were not sailing into entirely unknown waters. They were not so much survey missions as 'commercial exploration' and flag showing. When it comes to cargo capacity and sheer coolness factor, the great treasure junks could give value for money.

And most of all to the point, China had perhaps 50 times the resources of Portugal. A timely and interesting link from Winch of Atomic Rockets gives estimated GDPs in 1600. Portugal is not listed, but Spain and China are: Ming China, $96 billion; Philip II's Spain, $7.4 billion. Portugal a century earlier would have been at most perhaps $2 billion. Sending out a few hundred men aboard a squadron of caravels was as heavy a burden on Portugal as sending 30,000 men aboard a treasure fleet was for China.

So why did Portugal's program of exploration succeed, while China's was cancelled and forgotten? The reason can't be things like decentralization versus centralization or government versus private initiative. Both were more or less the same on those counts, pushed by government factions and supported by the merchants, shipbuilders, and such who benefited.

There are no doubt a host of other factors. The Chinese court eunuchs had domestic rivals who wanted to cut them down to size, while Henry the Navigator was a royal younger son who seemed out to make none of the trouble that royal younger sons can make.

But I believe the more important reason is that the Chinese treasure fleets had absolutely nothing to do with broader Chinese concerns of the time. The Indian Ocean produced nothing that the Chinese wanted the way Europeans wanted pepper, and it was irrelevant to the empire's security concerns. (Whereas central Asia was all too relevant.) Seafaring itself was incidental to most of China's population.

It was much different with Portugal, a small country with a substantial fishing population that would readily go to sea for anything more profitable. More important, Portugal shared the reconquista heritage and crusading enthusiasm of neighboring Castile, and shared with much of Western Europe a late medieval fascination with knighthood and quests that gave us Sir Thomas Malory's Le Mort d'Arthur.

Gold, spice, landed estates, adventures in exotic lands, and fighting Muslims (in a pinch, any 'paynims' would do) all got swirled together in the late medieval European imagination, and it was a powerful high. In literature it would produce Amadis of Gaul and his endless successors, the fantasy quest adventures of the 16th century. In retrospect it was embarrassing and often worse, but it had big consequences. It explored the world and conquered a fair part of it.

Pepper would help. But ultimately we will be propelled into space by the power of cool.

Monday, December 7, 2009

Future generations may have their share of mirth over the choice of name, particularly in our current less than chaste era. They can also ponder the iconography of the logo, a young woman in a tastefully impractical spacesuit. I hope they have a good laugh, because that will mean that SpaceShipTwo did well enough to be remembered.

I've had mixed feelings in the past about suborbital tourism, which is in some ways a gimmick, less demanding by an order of magnitude (at least!) than getting into orbit, the real ticket to Space. On the other hand it can't hurt, and may be a proving ground for technologies and streamlined operating procedures that will in time allow cheaper orbital flight.

Friday, December 4, 2009

This week the Sky & Telescope website gives us not one but two chances to indulge in gratuitous astronomical violence.

The first is a supernova detected in a remote galaxy in 2007, estimated to be about 100 times more powerful than mere 'ordinary' supernovae. A star of about 150 to 240 solar masses blew itself entirely apart. No remnant neutron star, no black hole, no nothing, just the expanding fireball.

They don't make bangs like that in our galaxy any more, not for the last few billion years. To get them you need stars of enormous mass that form only in the first generation, when there are no elements heavier than helium. The observed supernova is probably in a dwarf galaxy only just now forming stars. In our part of the universe the only remnants of these high power blasts are ... us. (And planets, etc.)

But our home galaxy is still perfectly capable of lesser bangs from conventional supernovae, and a prime candidate is Eta Carinae. In the 19th century it flared up for several decades to become one of the brightest stars in the sky, then faded to 5th magnitude. The Hubble image tells the story: a vast eruption, its expanding cloud now partly concealing the massive binary star within.

Evidence points to 'a new unstable phase of mass loss,' which sounds duly ominous. And all you have to do is look at the image to see that Eta Carinae, like a bad girl in a Victorian novel, is heading for a tragic but spectacular fate.

Tuesday, December 1, 2009

The space banquet has been troubled by the ghost of Leif Ericson all along, archeological confirmation of Norse voyages having been unearthed right at the start of the space age. Only some years later (at least for Westerners) did another ghost turn up at the feast: Zheng He, the Muslim eunuch who led the great Chinese 'treasure fleets' to the Indian Ocean nearly a century before the Portuguese got there from the other direction.

The Chinese may have gone farther than that. A 15th century Venetian monk and geographer, Fra Mauro, reported that a large 'zoncho' - junk - from the Indian Ocean sailed sailed 2000 miles into the Atlantic before turning back. The illustration on his map shows a ship of European type, but the artist was probably working from a second or third hand account, and knew only that the 'zoncho' was big.

(By the way, the Chinese probably did not 'discover America' in 1421 or any other year. File that one alongside the aliens who built the Pyramids.)

One puzzle about the treasure fleets turns out to have a simple (likely) explanation. The largest ships are reported to have been enormous, upwards of 150 meters long, even close to 200 meters. But Europeans later found that the maximum safe length for seagoing wooden ships was 60-70 meters, about 200 feet. Yes, the Chinese used very different constructional methods, but wood is wood, and early modern Europeans were not chumps when it came to wooden shipbuilding.

It is now thought that the mega junks were used only for river service on the Yangtze, while the largest ships in the treasure fleet were comparable in size to the largest European Indiamen a few hundred years later, with a load capacity of about 1500 tons. Which is just what you'd expect.

But the much bigger and sobering puzzle about the treasure fleets is the way their voyages suddenly ended. There was a power shift at the imperial court. The court eunuchs (among whom was Zheng He) had supported the voyages, and when they fell out of favor the budget ax soon fell. The treasure ships were laid up and left to rot away. More axes fell than that. Building large seagoing ships was forbidden, and China's entire maritime capacity rotted away. A hundred years later Europeans showed up, and the rest is history.

It makes a great cautionary story. Cut the NASA budget, and the next thing you know the red haired devils are at the door. Or something like that.

The real story is more complicated. For one thing, the treasure fleets were stupendously big and expensive. Really big, perhaps five or ten times the fleet tonnage of a Spanish treasure flota or a convoy of Indiamen. A vast and economically disruptive effort was called for to build the treasure fleets and send them out.

Imperial China was capable of it; whether it was a good idea was no doubt a matter of dispute. It was good if you were a merchant or timber supplier, or a member of the court with a taste for Indian or Middle Eastern luxuries, not so good if you were paying taxes for some fairly nebulous benefits.

So it is not surprising that there was a reaction. The whole enterprise had no deep foundations in China's economy or its political interests. It was a matter of imperial prestige, and only by one measure of prestige - fleets of junks impressed no one in Central Asia, far from any ocean. By comparison the British East India Company was deeply rooted in the folkways of England. (Crumpets and tea, anyone?)

The backlash, when it came, was as extravagant as the voyages themselves, but it did not cause the 'century of humiliation' 500 years later. Shipbuilding was banned, but the sky was big and the Emperor far away, and oceangoing Chinese shipbuilding did not cease. China lost the Opium Wars for other reasons, in another era.

If there is any warning here for space advocates it is about needless gigantism, and arguably the old hare and tortoise story. Perhaps the post-Apollo letdown was fortunate in that it happened early, before the inevitable backstroke could develop too much force. The post-Apollo program has been more modest, but in spite of setbacks it has proven fairly robust.